her final appearance as secretary of state comes today, when she introduces john kerry. and that is after her testimony about the attack in benghazi that killed a u.s. ambassador and three other americans. abc's martha raddatz was there for all of the action. good morning, martha. >> reporter: good morning, george. it was truly a riveting day on capitol hill. we don't say that very often, with secretary clinton. as some have never seen her before. she was at times, combative, charming, disarming and clearly ready for a fight. >> it is our job to figure out what happened and do everything we can to prevent it from ever happening again, senator. >> reporter: but when clinton spoke of her four fallen colleagues, the pain, the memories were still raw. >> i stood next to president obama as the marines carried those flag-draped caskets off the planes at andrews. i put my arms around the mothers and fathers, the sisters and brothers. the sons and daughters. >> reporter: and clinton did not hesitate to shoulder the blame. >> as i have said many times, i take responsibility. >> r